1. Field of the Invention
The invention generally relates to the field of anti-tamper fabrication and assembly approaches for electronic circuits and microelectronic packages.
More specifically, the invention relates to an electrical coupling method and device for use with electronic circuits or modules that are enclosed in an anti-tamper wrapper or mesh for the sensing of an attempt to tamper with the circuit or module within the wrapper.
2. Description of the Related Art
It is a known concern of military and commercial entities that reverse engineering and evaluation of an electronic circuit can occur when the electronic circuit (e.g., a microelectronic circuit) falls into enemy hands or into the possession of a business competitor. The U.S. Government has expressly noted such a concern in a directive entitled, “DoD Directive 5200.39, “Research and Technology Protection within the Department of Defense,” issued in March 2002.
Military opponents or commercial competitors can gain an advantage by learning the operation and vulnerability of a circuit by electronic probing or by physically examining the circuit such as using X-ray or by mechanically or chemically removing circuit or package structures to understand and view the circuit in order to duplicate or develop methods of defeating it.
In view of the above, having means in place to make the reverse engineering of a protected circuit difficult or impossible without complex test equipment is needed. Such protection is needed to minimize the risk an adversary can learn key features and functions of a protected circuit and develop means to disable or imitate the device.
One such anti-tamper method is described in U.S. Pat. No. 7,947,911, issued May 24, 2011 and entitled, “Anti-Tamper Mesh” which describes a method of forming an anti-tamper mesh on an electronic device. The method described includes forming at least one terminal on the electronic device and forming a conductive mesh on at least one surface of the electronic device, wherein the conductive mesh is in electrical contact with the terminal, and wherein the terminal facilitates electrical conduction between the conductive mesh and an electrical detection circuit wherein tampering with the conductive mesh is detected by the circuit.
In a typical anti-tamper circuit, i.e., a protected circuit, upon detection of a tamper event, a predetermined tamper response is generated, i.e., a protected circuit will take some action when unauthorized activities are detected. Any number of events can be used to sense and trigger a predetermined circuit response. Examples of active triggering events may include: voltage, photon detection, acceleration, strain, thermal, chemical attack, and proximity or tamper-respondent enclosures. A tamper-respondent package is used to detect unauthorized probing by proximity detection or by an external activity mutilating an active circuit, exterior to what is being protected. The response of an active anti-tamper circuit upon triggering is also widely variable. For example, data zeroization may be employed in which critical memory cells or an entire die can be erased. Similarly, a response can trigger overwriting of some or all of a memory die. Another detection response is to physically obliterate a critical circuit element or elements such as by use of a FET switch or fusible link embedded in the circuit.
Anti-tamper meshes are available for wrapping or enclosing a circuit package or module wherein the mesh structure is a sheet comprising a plurality of electrically conductive metal traces, the breaking or shorting of which are used to generate a tamper response. The meshes are provided with a grid or matrix of exposed conductive mesh pads of a predetermined pitch and spacing for electrical coupling to the device to be protected where the device has a matching set of conductive device or module pads that have substantially the same pitch and spacing as the mesh pads. Because the pitch and spacing of the mesh pads is small and the tolerances and precision needed to connect the mesh pads to the device or modules pads is high, the electrical coupling of the mesh to the protected device is difficult.
What is needed is a low-cost, reliable method for the interconnection of the mesh conductive pads to the pads of the protected device.